Dense substrate for solid oxide fuel cell

ABSTRACT

A dense substrate for a solid oxide fuel cell, comprising: a base portion, support portions and fixing portions all of which project from the base portion so as to be arranged sequentially in one direction; grooves formed between the support portions and the fixing portions or between the support portions; and mount portions which are provided on the support portions between the fixing portions for mounting and fixing at least cell sections thereon. A solid oxide fuel cell is easily manufactured at a reduced cost by arranging a plurality of cell sections and, if required, plate sections, on the mount portions of the above dense substrate; fixing the cell sections and, when used, plate sections, onto the mount portions with an insulating bonding agent; and joining adjacent cell sections together with interconnections.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a dense substrate for a solid oxide fuel cell(which will hereinafter be referred to as SOFC) in which anelectrochemical reaction is carried out to take out electric energy, asolid oxide fuel cell using the same substrate, and a method ofmanufacturing the same solid oxide fuel cell.

2. Description of the Prior Art

There are known SOFC's which include a tubular SOFC (Japanese PatentLaid-Open No. 73246/1979) formed by providing a plurality of singlecells, each of which consists of a fuel electrode, electrolyte and anair electrode, on the outer surface of an elongated cylindrical poroussupport tube, and connecting the single cells in series, and amonolithic SOFC (Japanese Patent Laid-Open No. 100376/1985) formed bysandwiching a flat cell section, which consists of three layers of afuel electrode, an electrolyte and an air electrode, between corrugatedmutual-connection walls each of which consists of three layers of an airelectrode, an interconnection and a fuel electrode.

Regarding the practical use of SOFC's a tubular SOFC can be manufacturedcomparatively easily but a support tube cannot be made extremely thin inview of the structure thereof. Therefore, this type of SOFC does nothave as high of an output performance per volume. A monolithic SOFC hasa high output performance per volume but involves very difficultmanufacturing problems in the production of a cell, a gas sealing,assembling, etc. The inventors of the present invention then filed apatent application, i.e. Japanese Patent Application No. 106610/1990,which has been laid-open to public inspection under Laid-Open No.6752/1992, for the solid oxide fuel cell disclosed therein, so as tosolve these problems. According to this invention, the portion of adense substrate to which a cell section is to be fixed is subjected to amechanical boring process. Carrying out this process is difficult, andpresents a problem concerning the dimensional accuracy thereof.

Moreover, in a conventional method of this kind, a plurality of cellsections are manufactured simultaneously or assembled unitarily at atime. Consequently, when a failure occurs in one cell section, there isthe possibility that the whole assembly cell stacks or cell sectionsbecome unusable.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a highlyreliable SOFC which permits the formation of cell mount portions of adense substrate without carrying out a boring process therein, andtherefore is capable of being manufactured easily and at a reduced cost,a method of manufacturing the same SOFC, and a dense substrate for thesame SOFC.

In order to solve the above problems, the inventors of the presentinvention have earnestly studied the construction of a dense substrateto obtain the knowledge that it is effective to provide grooves in adense substrate and arrange cells, which have been produced in advance,in these grooves, and come to achieve the present invention.

The present invention is as follows:

(1) A dense substrate for a solid oxide fuel cell, comprising: a baseportion, support portions and fixing portions, all of which project fromthe base portion so as to be arranged sequentially in one direction;grooves formed between the support portions and the fixing portions andbetween the support portions; and mount portions which are provided onthe support portions between the fixing portions for mounting andaffixing at least cell sections thereon.

(2) A solid oxide fuel cell having a plurality of cell sections and, ifrequired, a plurality of plate sections, on the mount portions of thedense substrate defined in (1) above, the cell sections and the mountportions being joined together by an insulating bonding agent, adjacentcell sections being joined together by interconnections.

(3) A method of manufacturing a solid oxide fuel cell, comprising thesteps of:

arranging a plurality of cell sections and, if required, plate sections,on the mount portions of the dense substrate defined in (1) above;

fixing the cell sections and, when used, plate sections, onto the mountportions with an insulating bonding agent; and

joining adjacent cell sections together with interconnections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the dense substrate according to thepresent invention and the relation of arrangement between cell sectionsand plate section mounted thereon.

FIG. 2 is a plan view showing the outline of Example 1 of the SOFCaccording to the present invention.

FIG. 3 is a cross-sectional view of the SOFC taken along the line Y--Yof FIG. 2.

FIG. 4 is a cross-sectional view of the SOFC taken along the line X--Xof FIG. 2.

FIG. 5 is a plan view showing the outline of Example 2 of the SOFC.

FIG. 6 is a cross-sectional view of the SOFC taken along the line Y--Yof FIG. 5.

FIG. 7 is a cross-sectional view of the SOFC taken along the line X--Xof FIG. 5.

FIG. 8 is a perspective view of a cell section using a porous airelectrode base.

FIG. 9 is a perspective view of a cell section using a porous fuelelectrode base.

FIG. 10 is a perspective view of a cell section formed by laminating anair electrode, an electrolyte and a fuel electrode in the mentionedorder on a porous support base.

FIG. 11 is a perspective view of a cell section formed by laminating afuel electrode, an electrolyte and an air electrode in the mentionedorder on a porous support base.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of a dense substrate 1 for a solid oxide fuel cell accordingto the present invention is shown in FIG. 1. Referring to FIG. 1, areference numeral 2 denotes a base portion, 3 fixing portions, 4 supportportions, 5 grooves and 6 mount portions provided between the fixingportions and on the support portions. As is clearly noted from FIG. 1,in the solid oxide fuel cell according to the present invention, aplurality of cell sections 7 are mounted on and fixed to the mountportions 6 on the support portions 4 projecting from the base portion 2of the dense substrate 1, and the fixing portions 3 also projecting fromthe base portion 2. A dense plate section 8 is provided as necessary onan end portion of the dense substrate 1 or between the cell sections 7.The cell sections and plate sections are affixed to the dense substrate1 by an insulating bonding agent. Consequently, hollow portions 15 areformed, which are defined by the grooves 5, cell sections 7 and platesections 8, in the dense substrate 1.

A first type of cell section produced in advance so as to be used in thepresent invention is formed, as shown in FIGS. 8 and 9, by laminating ona porous base of an electrode material, which consists of either aporous air electrode base 11 or a porous fuel electrode base 16, anelectrolyte film 12 and then another electrode film, i.e. a fuelelectrode film 13 or an air electrode film 17. A second type of cellsection is formed, as shown in FIGS. 10 and 11, by laminating an airelectrode film 17 (or a fuel electrode film 13), an electrolyte film 12and a fuel electrode film 13 (or an air electrode film 17) in thementioned order on a porous base 18 which constitutes a support body.

In the above example, the hollow dense substrate 1 consists preferablyof a ceramic material, an electrically insulating material, and, forexample, alumina, magnesia or a mixture thereof are suitably used.

The electrolyte film 12 consists suitably of yttria-stabilized zirconia(which will hereinafter be referred to as YSZ). The porous electrodebase and electrode film consisting of an air electrode film are suitablycomposed of alkaline earth metal-added LaMnO₃ and LaCoO₃, and the porouselectrode base and electrode film consisting of a fuel electrode filmNi-zirconia cermet.

The porous base 18, which is to constitute a support body, consistspreferably of a porous ceramic material. For example, alumina, magnesia,a mixture thereof and stabilized zirconia are suitably used, and it ismore desirable that electronic conductivity be provided to the porousbase if possible.

The cell sections 7 produced in advance are placed on the mount portions6 between the fixing portions 3, 3 of the dense substrate 1 bypreferably fitting the former on the latter, and then affixed, and theelectrodes of adjacent cell sections are connected in series and inparallel by interconnections. When the dense substrate and cell sectionsand the adjacent cell sections are joined together with an insulatingbonding agent to form interconnections, an SOFC having excellent gassealability can be obtained.

When a gas sealing film 14 is formed in the fitted portion and aninterconnection thereafter is formed, or, when a cell section is affixedto an insulating bonding agent and, then, a gas sealing film and aninterconnection are formed in that order, an SOFC having a higher gassealability can be obtained.

The interconnection referred to above consists suitably of a materialhaving electronic conductivity and which is stable in anoxidation-reduction atmosphere, for example, a perovskite oxide obtainedby adding an alkaline earth metal to LaCrO₃.

The bonding agent consists preferably of a material which is stable inan oxidation-reduction atmosphere, has insulating characteristics and iscapable of being densified, such as a ceramic material includingalumina, silica and zirconia, and the gas sealing film an electricallyinsulating material, such as alumina.

Out of the structural elements of the SOFC, the hollow dense substrateis formed by extrusion, and the porous electrode base and porous supportbase by a doctor blade method and a powder pressing method.

The electrode film, electrolyte film, interconnection and gas sealingfilm are formed by film forming techniques including dry type methods,such as plasma spray, gas flame spray, CVD and PVD, and wet typemethods, such as a screen printing method and a dipping method.

An SOFC according to the present invention in which the porous electrodebase for cell sections consists of an air electrode will now bedescribed. When oxygen is supplied to the hollow portions of the densesubstrate while supplying hydrogen to the outer portion of the densesubstrate, which is on the side of the fuel electrode, with the SOFCmaintained at about 1000° C., an electrochemical reaction occurs togenerate electric energy.

According to the present invention, the following effects can beobtained.

(1) Since the cell sections are produced in advance, an imperfect cellsection can be rejected, and perfect cell sections only can be set onthe dense substrate. Therefore, the yield and reliability of the SOFCare improved.

(2) Since cell sections produced in advance are set on a densesubstrate, the dense substrate does not receive the influence of theprocessing heat used during the formation of electrode films andelectrolyte films, unlike the case where cell sections are formed by avapor deposition method or a spray method on a dense substrate, so thereliability of the SOFC is improved.

(3) Since the cell section has a simple construction and can bemass-produced simply and mounted on a dense substrate easily, themanufacturing cost decreases.

(4) The fixing portions, support portions, mount portions and grooveswhich are used to set and fix cell sections can be formed integrallywhen a dense substrate is extruded. Therefore, the manufacturing stepsare simplified. Further, unlike a conventional SOFC, the SOFC accordingto the present invention does not require a process for boring asubstrate. This also enables the manufacturing cost to decrease.

EXAMPLE 1

A first embodiment of the present invention will now be described withreference to the drawings.

FIG. 2 is a plan view showing the outline of an SOFC as a whole, andFIGS. 3 and 4 are sectional views taken along the lines Y--Y and X--X,respectively.

The dense substrate 1 was formed from a raw material, i.e. alumina, byextrusion, and then fired at 1400°-1700° C. A method of manufacturingthe cell section 7 will now be described. First, a green film was formedfrom La₀.8 Sr₀.2 MnO₃ by a doctor blade method, and the film was thencut into pieces with a cutter. The cut pieces were fired at 1200°-1500°C. to obtain porous air electrode bases 11. The porous air electrodebase 11 was then masked to form a current takeout portion, and yttriastabilized zirconia was then sprayed onto the base 11 by a plasma spraymethod to form an electrolyte film 12. Finally, the upper surface of theelectrolyte film 12 was masked, and NiO-YSZ was then sprayed onto theelectrolyte film 12 by a gas flame spray method to form a fuel electrodefilm 13 and complete the production of a cell section 7.

A plurality of cell sections 7 thus produced were affixed to the fixingportions 3 and mount portions 6 of the dense substrate 1 by an aluminabonding agent 9. If necessary, dense plate sections 8 were then affixedto the portions of the dense substrate 1, which were adjacent to thecell sections 7, by an insulating bonding agent. In this embodiment, 25cell sections were affixed to one surface of the dense substrate 1,which were then masked, and LaMgCrO₃ was thereafter sprayed onto thedense substrate 1 by a plasma spray method or a gas flame spray methodto form interconnections 10, the cell sections 7 being connected inseries and in parallel. After the cell sections have been affixed to onesurface of the dense substrate 1, the other surface was subjected to thesame operations to produce an SOFC.

EXAMPLE 2

A second embodiment will now be described with reference to FIGS. 5, 6and 7.

FIG. 5 is a plan view showing the outline of an SOFC as a whole, andFIGS. 6 and 7 are sectional views taken along the lines Y--Y and X--X,respectively. The gas sealing films 14 shown in the drawings were formedby spraying alumina by a plasma spray method after the cell sections 7had been affixed to the dense substrate 1 and before theinterconnections 10 had been formed. The other materials used and themanufacturing method employed were the same as those in Example 1.

An electric current can be generated by supplying oxygen to the hollowportions 15 defined by the dense substrate 1, cell sections 7 and denseplate section 8, and hydrogen to the fuel cell side portion of thecompleted SOFC, with the SOFC maintained at about 1000° C.

The shapes of the dense substrate 1, cell sections 7, dense platesection 8 and masking films are not limited to those of the parts in theabove-described embodiments; they may be formed in other shapes. Theeffect of an SOFC which uses a porous support base for the cell sections7, owing to the above-described manufacturing method, and that of anSOFC provided with fuel electrodes on the side of the hollow portions 15thereof, owing to the same method, are identical to each other.

As described in detail above, the portions of a conventional densesubstrate to which cell sections are to be affixed are subjected to aboring process (mechanical process), so that a conventional densesubstrate has processing difficulty and problems concerning thedimensional accuracy thereof. On the other hand, the dense substrateaccording to the present invention can be manufactured easily and in ahigh yield by, for example, extrusion (molding), and enables thereduction of the manufacturing cost. Since this dense substrateconsisting of a fragile material does not require a boring process, ithas a high dimensional accuracy. In the solid oxide fuel cell, cellsections produced in advance are set on a dense substrate, andinterconnections or gas sealing films and interconnections are thenformed. Therefore, imperfect cell sections can be rejected before anSOFC has been assembled, and the dense substrate receives littleinfluence of processing heat. This enables the yield and reliability ofthe SOFC to be improved. Moreover, according to the manufacturing methodof the present invention, the production of solid oxide fuel cell can becarried out with a high efficiency, and this method is suitable for themass production of the same products and enables the yield thereof to beimproved.

What is claimed is:
 1. A solid oxide fuel cell having a plurality ofcell sections on mount portions of a dense substrate, said densesubstrate comprising: a base portion, support portions and fixingportions all of which project from said base portion so as to bearranged sequentially in one direction; grooves formed between saidsupport portions and said fixing portions and between said supportportions; and said mount portions which are provided on said supportportions between said affixing portions for mounting and fixing at leastcell sections thereon, wherein said cell sections and said mountportions are joined together with an insulating bonding agent andadjacent cell sections being joined together with interconnections. 2.The solid oxide fuel cell according to claim 1 wherein each of said cellsections comprises a porous electrode base selected from the groupconsisting of a porous air electrode base and a porous fuel electrodebase, an electrolyte film laminated on said porous electrode base and anelectrode film laminated on said electrolyte film.
 3. The solid oxidefuel cell according to claim 2, wherein said porous electrode baseprojects laterally a distance beyond said electrolyte film and saidelectrolyte film projects laterally a distance beyond said electrodefilm thereby exposing a portion of an upper surface of each of saidporous electrode base and said electrolyte film.
 4. The solid oxide fuelcell according to claim 1 wherein each of said cell sections comprises aporous base, a first electrode film laminated on said porous base, anelectrolyte film laminated on said first electrode film and a secondelectrode film laminated on said electrolyte film.
 5. The solid oxidefuel cell according to claim 4 wherein said first electrode film isselected from the group consisting of an air electrode film and a fuelelectrode film.
 6. The solid oxide fuel cell according to claim 4wherein said second electrode film is selected from the group consistingof an air electrode film and a fuel electrode film.
 7. The solid oxidefuel cell according to claim 4 wherein said first electrode filmprojects laterally a distance beyond said electrolyte film and saidelectrolyte film projects laterally a distance beyond said secondelectrode film thereby exposing a portion of an upper surface of each ofsaid first electrode film and said electrolyte film.